PyGrunn: descriptors, decoding the magic - Alex Dijkstra¶

Tags: pygrunn, python

(One of my summaries of the 2024 Dutch PyGrunn python&friends conference in Groningen, NL).

“Descriptors” are re-usable @property-like items. They implement the __get__, __set__ and __delete__ methods and possibly the __set_name__ method.

See https://docs.python.org/3/howto/descriptor.html for an introduction on the python website.

Most of the talk consisted of code examples: I’m not that fast a typer :-) So this summary is mostly a note to myself to check it out deeper.

You can use them for custom checks on class attributes, for instance. Or for some security checks. Or for logging when an attribute is updated.

This is how it looks when you use it:

class Something:
    id = PositiveInteger()  # <= this is your descriptor

So usage of a descriptor is easy. The hard and tricky part is actually writing them. If you don’t really need them: don’t try to write them. If you write code that is used a lot, the extra effort might pay off.

A funny one was an Alias descriptor:

class Something:
    name: str
    full_name = Alias("name")
    nickname = Alias("name")

something = Something()
something.name = "pietje"
something.name  # Returns pietje
something.full_name  # Returns pietje, too
something.nickname  # Returns pietje, too